(1) Field of the Invention
This invention relates to surface treatment of a semiconductor substrate, i.e., a wafer. More particularly, it relates to a method for roughening a surface of a semiconductor substrate by an etching technique.
(2) Description of the Prior Art
In order to reduce the thermal resistance and collector parasitic resistance of a semiconductor device, or enhance the adhesion strength of a semiconductor element to an electrode metal or to a package, it is necessary, in the course of manufacturing the semiconductor device, to reduce the thickness of the semiconductor substrate to the desired value, i.e., usually 100 to 200 microns, and further, to roughen the back surface of the semiconductor substrate. By the term "back surface", used herein, is meant a surface of the semiconductor substrate opposite to the surface at which circuit elements formed in the substrate are exposed. The above-mentioned reduction in thickness and roughening of the back surface have been heretofore effected by sanding the back surface of the semiconductor substrate by using an abrasive material and a sanding machine. It is unavoidable, however, that the so-sanded semiconductor substrate is subjected to an etching treatment to remove the residual abrasive material from the substrate and, also, to remove the strained thin surface layer from the substrate. Such an etching treatment undesirably smooths the roughened back surface to some extent and requires a substantially long period of time. Furthermore, the size of the semiconductor substrate has recently become large, i.e., its diameter being from 75 to 100 mm. Therefore, the above-mentioned sanding of the semiconductor substrate is liable to damage the semiconductor substrate and, thus, the sanding operation requires special caution and is troublesome.